The retrotrapezoid nucleus neurons expressing Atoh1 and Phox2b are essential for the respiratory response to CO₂.

Pierre-Louis Ruffault,John A Hayes,Mikio Hoshino,Christo Goridis,Fabien D'Autréaux,Martin Hägglund,Gilles Fortin,Tomoyuki Fujiyama,Jean-François Brunet,Sandra Autran,Ole Kiehn,Marc Nomaksteinsky

doi:10.7554/elife.07051

Abstract

Maintaining constant CO2 and H(+) concentrations in the arterial blood is critical for life. The principal mechanism through which this is achieved in mammals is the respiratory chemoreflex whose circuitry is still elusive. A candidate element of this circuitry is the retrotrapezoid nucleus (RTN), a collection of neurons at the ventral medullary surface that are activated by increased CO2 or low pH and project to the respiratory rhythm generator. Here, we use intersectional genetic strategies to lesion the RTN neurons defined by Atoh1 and Phox2b expression and to block or activate their synaptic output. Photostimulation of these neurons entrains the respiratory rhythm. Conversely, abrogating expression of Atoh1 or Phox2b or glutamatergic transmission in these cells curtails the phrenic nerve response to low pH in embryonic preparations and abolishes the respiratory chemoreflex in behaving animals. Thus, the RTN neurons expressing Atoh1 and Phox2b are a necessary component of the chemoreflex circuitry.

Highlights

In mammals, breathing is the prime homeostatic process that regulates CO2 partial pressure (PCO2) in the blood
Photoactivation of the embryonic retrotrapezoid nucleus (RTN) entrains the respiratory motor output We first verified the ability of embryonic RTN neurons to entrain the respiratory-like motor output using channelrhodopsin-based optogenetics
The RTN neurons have been implicated in breathing regulation by CO2, but their importance for the respiratory chemoreflex in the intact brain remains controversial (Huckstepp and Dale, 2011; Nattie, 2011; Guyenet et al, 2013)

Summary

Introduction

In mammals, breathing is the prime homeostatic process that regulates CO2 partial pressure (PCO2) in the blood. The respiratory chemoreflex modulates ventilation in response to deviations in arterial or brain PCO2, mainly through the detection of changes in pH (Feldman et al, 2003; Guyenet et al, 2010). These changes are sensed by central chemosensors located in the brainstem and by the carotid bodies in the periphery, but most of the CO2 chemosensory drive to breathe is thought to arise centrally (Smith et al, 2006; Duffin, 2010).

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